In typical cellular wireless communication systems, wireless communication devices (WCDs) (e.g., cell phones, personal digital assistants, laptops, netbooks, tablets, and/or other wirelessly equipped devices) subscribe to service from a given cellular wireless service provider. In practice, a cellular wireless service provider will operate one or more radio access networks (RANs) including base transceiver stations (BTSs) that radiate radio frequency (RF) patterns to define wireless coverage areas where the subscriber WCDs can operate.
Within each coverage area, the radiated RF pattern may provide one or more wireless links over which a WCD can obtain connectivity to broader networks such as the public switched telephone network (PSTN) and the Internet. Further, each RAN may include one or more radio network controllers (RNCs) or the like, which may be integrated with or otherwise in communication with the BTSs, and which may include or be in communication with a switch or gateway that provides connectivity with one or more transport networks. Conveniently with this arrangement, a WCD that is positioned within coverage of the RAN can then communicate with a BTS and in turn, via the BTS, with other served devices or with other entities on the transport network.
The wireless links may carry communications between the RAN and the WCDs according to any of a variety of wireless protocols. Depending on the protocol employed, each wireless link may also be divided into a plurality of channels for carrying communications between the RAN and the WCDs. For example, each wireless link may include a plurality of forward link channels, such as forward traffic channels, for carrying communications from the RAN to the WCDs. As another example, each wireless link may include a plurality of reverse-link channels, such as reverse traffic channels, for carrying communications from the WCDs to the RAN.
In many wireless protocols, the RAN and WCDs that are actively communicating with the RAN (“active WCDs”) may engage in a power-control process to control transmission power for communications over established traffic channels. In an example forward-link power control process, an active WCD may regularly send power control commands (PCCs) (e.g., a “power up” command or a “power down” command) directed to the RAN, to control the RAN's transmission power on a forward traffic channel to the active WCD. For example, during a communication session between an active WCD and the RAN, the active WCD may regularly compare the power level of received transmissions to a power level set point and thereby decide whether to send a power up command that instructs the RAN to increase its forward transmission power to the active WCD or a power down command that instructs the RAN to decrease its forward transmission power to the active WCD.
For instance, if the received power level of the active WCD is less than the active WCD's power level set point, the active WCD may send a power up command directed to the RAN. Alternatively, if the received power level of the active WCD is greater than the active WCD's power level set point, the active WCD may send a power down command directed to the RAN.
A WCD may adjust the power level set point up or down based on a variety of computations. One such computation is a communication error rate computation. For example, during a communication session between an active WCD and the RAN, the active WCD may regularly calculate a rate of communication errors in the forward traffic-channel communications received from the RAN. The active WCD may compare the calculated communication error rate to a target communication error rate and thereby decide whether to increase or decrease the WCD's power level set point.
For instance, if a WCD's calculated communication error rate is greater than the WCD's target communication error rate, the WCD may increase the WCD's power control set point. Alternatively, if a WCD's calculated communication error rate is less than the WCD's target communication error rate, the WCD may decrease the WCD's power control set point.
Typically, an active WCD will send PPCs to the RAN more frequently than the active WCD adjusts the power control set point. For example, an active WCD may send to the RAN 800 PCCs per second, whereas the active WCD may adjust the power control set point twice per second. Other rates of sending PCCs and adjusting power control set points are possible as well.
Additionally, a similar power control process may carried out by the RAN to control the reverse-link transmission power of each WCD.
As a result of active WCDs regularly sending PCCs directed to the RAN, the RAN may regularly receive PCCs from active WCDs. (It should be understood, however, that the RAN may fail to receive some PCCs sent by the active WCD due to poor reverse-link conditions or other factors.) In response to each PCC received from the active WCD, the RAN may then responsively adjust its forward link transmission power to the active WCD in accordance with the PCC. For instance, in response to receiving a power up command from the active WCD, the RAN may increase its forward link transmission power to the active WCD. And in response to receiving a power down command from the active WCD, the RAN may decrease its forward link transmission power to the active WCD.
In some protocols, the RAN may have a limit on the total amount of transmission power the RAN can use in a given coverage area. Such a limit is referred to as the “maximum allowable power level.” The maximum allowable power level may be set by a system designer or system operator, with one example being 80 watts (though other examples are possible as well).
Similarly, the RAN may have a limit on the amount of forward link transmission power the RAN can use for transmission to any one WCD. For instance, the RAN may maintain a “channel-maximum” power parameter that defines this limit (e.g., 2.4 watts per WCD). Alternatively, the RAN may have a separate channel-maximum power parameter for each individual traffic channel, with the parameters possibly taking on different values (e.g., 2.4 watts for a first traffic channel and 2.0 watts for a second traffic channel).